Chain tensioner



United States Patent 3,463,025 CHAIN TENSIONER Edward C. Turner, Hitchin, and John Poyser, Letchworth,

England, assignors to Borg-Warner Corporation, Chicago, Ill., a corporation of Delaware Filed May 27, 1968, Ser. No. 732,256 Claims priority, application Great Britain, June 5, 1967, 25,766/ 67 Int. Cl. F16h 7/08 US. Cl. 74-24211 9 Claims ABSTRACT OF THE DISCLOSURE A chain tensioner has an arcuate shoe of synthetic plastics material which will creep under load and elevated temperature. The shoe engages the chain to be tensioned, and is secured to a slidable member. Its ends are urged towards each other by a spring to bulge the shoe to engage the chain and a non-return mechanism is attached to the shoe to allow the ends to move apart but prevent them moving towards each other.

This invention relates to a chain tensioner and is an improvement over the invention disclosed in our British Patent No. 986,174.

According to the present invention, a chain tensioner comprises an arcuate shoe of synthetic plastics material which will creep under load and elevated temperature secured to a slidable member and whose ends are urged towards each other by spring means to bulge the shoe into engagement with the chain to be thereby tensioned, and a non-return mechanism attached to the shoe to prevent the ends thereof moving apart while allowing them to approach each other.

The invention will be better understood from the following particular description of an illustrative embodiment thereof, given with reference to the drawings 1n which:

FIG. 1 is a plan view of one form of chain tensioner according to the invention, and

FIG. 2 is a side elevation corresponding to FIG. 1.

The illustrated chain tensioner is intended for employment in an internal combustion engine. It includes a chaincontacting shoe 10 of synthetic plastics material, for example a rigid filled nylon such as that known as Nylatron supplied by Messrs. Polypenco Ltd., and this shoe is pivotally secured by pivot pin 12 at one end to a slidable member 14, and has a bore 16 at the other end to receive a fixing bolt or pivot pin. The synthetic plastics shoe 10 has longitudinal stilfening ribs 20, and its central region is connected by a pivot pin 22, a pair of pivotable links 24 and a pivot pin 26 to the inner end of the slidable member 14. The member 14 is adapted to slide on a suitable fixed support 28, this being secured in relation to the chain drive and the associated engine as may be convenient.

A rod 30 is pivotally attached, by means of a pin and slot connection (32, 34), to the shoe 10 towards the end 16 thereof, and the shoe is provided with an elongated slot 32 to receive the pivot pin 34. A slidable member in the form of a sleeve 38 encircles and can slide along the rod 30, and this sleeve 38 is pivotally mounted on the slidable member by the pin 26 and has an integral extension 40 rigid therewith. The extension 40 has a hole 42 into which one end of spring means in the form of a tension spring 44 is located. The other end of the spring 44 is secured to the shoe 10 by a pin or bolt 46. The elfect of the spring is to cause the sliding sleeve 38 to pivot in a clockwise direction as seen in FIG. 2, in a plane occupied by the rod 30. This has the result that "ice when the member 14 moves to the right and the shoe 10 becomes more bowed, as occurs during the desired operation of the chain tensioner, the sleeve 38 can slide along the rod in a direction to the right as seen in the figure. However, because of the rotary effect of the spring 44 on the sleeve 38 and the friction between rod 30 and sleeve 38, the sleeve 38 cannot slide towards the left and in consequence a relaxing of the chain tensioning device is prevented. In this way, it will be seen that the spring 44, rod 30, and sleeve 38 constitute a non-return mechanism, assuring that the chain of the chain drive with which this device is used will be adequately tensioned during normal operation, even though a kick-back, i.e. a reversal of movement of the chain, should occur. This has been found to be a particular problem with internal combustion engines of the larger, V12 design, and it will be appreciated that failure of a chain tensioning device to maintain tension upon kick-back may have serious consequences, in that the drive chain may become so slack momentarily that it can become disengaged from one of its sprockets.

The function of the elongated slot 32 at the end of the rod 30 is to provide a certain amount of lost motion so that a minor amount of movement of the synthetic plastics shoe 10 can take place before the non-return mechanlsm comes into action.

In one advantageous embodiment of the invention, a rod 30 of approximately 4 inch was employed with a sleeve member 38 bored out to about 2-8 thousandths of an inch clearance relative to the rod. The sleeve in that example was about 0.15 inch in axial length, that is to say in the direction of the rod axis. In general, the rod diameter should be from 1 /2 to 3 times, preferably about twice, the axial length of the sleeve member. The best sleeve-rod clearances will depend on the overall dimensions of the parts but a value between 2 and 15 thousandths of an inch will normally provide satisfactory operation.

It will be appreciated that modifications can be made within the scope of the invention. For example the nonreturn mechanism could be constituted by a rack having slanted teeth co-operating with a suitably spring-biased pawl. Any suitable synthetic plastics material may be used for the chain-contacting shoe.

The term synthetic plastics material used herein includes synthetic plastics material incorporating a filling or reinforcing material such as commonly used in such plastics materials.

We claim:

1. A chain tensioner comprising:

(A) an arcuate shoe of synthetic plastics material which will creep under load and elevated temperature;

(B) a member slidable on a support and secured to the said shoe;

(C) spring means connected between the ends of the shoe and operative in use to urge the ends of the shoe towards each other to bulge the shoe into engagement with the chain to be thereby tensioned; and

(D) a non-return mechanism attached to at least one end of the said shoe and operative to prevent the ends of the shoe moving apart while allowing them to approach each other.

2. A chain tensioner according to claim 1 wherein the shoe has longitudinal stiffening ribs.

3. A chain tensioner according to claim 1 wherein the non-return mechanism includes a sleeve-like member slidable in one direction but not the other along a rod.

4. A chain tensioner according to claim 3 wherein the spring means as one of its ends connected to the shoe and the other of its ends connected via the sleeve-like member and slidable member to the other end of the shoe, and wherein the connection of the spring means to the sleeve-like member is such that the sleeve-like member is biased to rotate in the plane occupied by the rod.

5. A chain tensioner according to claim 3 comprising a pair of links pivotally connecting the said slidable member and the said shoe.

6. A chain tensioner according to claim 3 comprising a lost-motion connection between the said rod and the said shoe.

7. A chain tensioner according to claim 6 wherein the shoe has walls defining an elongated slot therein and a pin adapted to be received in said slot is secured to the said rod.

8. A chain tensioner according to claim 3 wherein the the said sleeve-like member.

5 member is about 0.15 inch in length.

References Cited UNITED STATES PATENTS 2,141,118 12/1938 Weller 74-242.11

3,276,282 10/1966 Duncan 74442.11

FRED C. MATTERN, JR., Primary Examiner J. A. WONG, Assistant Examiner 

